Probably Nagato.
Any attempt Minato makes to get close to Nagato, with a kunai or trying to mark him, would be repelled by Shinra Tensei. It would be a difficult fight, since if Nagato tries to pull Minato towards him, Minato could just teleport away. However, based on what we've seen from both of them, Nagato has more chances of countering Minato's abilities and defeating him.
If we're factoring Minato's KCM into this, there's a chance he might be able to win, but he's still just as vulnerable in that mode.